[Bug math/18020] New: [ldbl-128ibm] asinhl inaccurate

[Bug math/18020] New: [ldbl-128ibm] asinhl inaccurate

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18020

            Bug ID: 18020
           Summary: [ldbl-128ibm] asinhl inaccurate
           Product: glibc
           Version: 2.21
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
          Assignee: unassigned at sourceware dot org
          Reporter: jsm28 at gcc dot gnu.org

The ldbl-128ibm implementation of asinhl uses cut-offs of 0x1p28 and 0x1p-29 to
determine when to use simpler formulas that avoid possible overflow /
underflow.  Both those cut-offs are inappropriate for this format, resulting in
large errors, e.g.:

Failure: Test: asinh (0x2p+28)
Result:
 is:          2.07944154167983592825e+01   0x1.4cb5ecf0a96504221a8bp+4
 should be:   2.07944154167983592834e+01   0x1.4cb5ecf0a96504231a8bp+4
 difference:  8.67361737988600762432e-19   0x1.00000000004000000000p-60
 ulp       :  2199023255552.5000
 max.ulp   :  1.0000

Failure: Test: asinh (0x4p-32)
Result:
 is:          9.31322574615478515625e-10   0x1.00000000000000000000p-30
 should be:   9.31322574615478515490e-10   0x1.fffffffffffffffaaaabp-31
 difference:  1.34632261157723174603e-28   0x1.55555555556000000000p-93
 ulp       :  5864062014805.5000
 max.ulp   :  1.0000

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[Bug math/18020] [ldbl-128ibm] asinhl inaccurate

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18020

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=137cef7d433407bd2ded8bcc5bea70e5858df47a

commit 137cef7d433407bd2ded8bcc5bea70e5858df47a
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Feb 25 11:13:41 2015 +0000

    Fix ldbl-128ibm asinhl inaccuracy (bug 18020).

    The ldbl-128ibm implementation of asinhl uses cut-offs of 0x1p28 and
    0x1p-29 to determine when to use simpler formulas that avoid possible
    overflow / underflow.  Both those cut-offs are inappropriate for this
    format, resulting in large errors.  This patch changes the code to use
    more appropriate cut-offs of 0x1p56 and 0x1p-56, adding tests around
    the cut-offs for various floating-point formats.

    Tested for powerpc.  Also tested for x86_64 and x86 and updated ulps.

        [BZ #18020]
        * sysdeps/ieee754/ldbl-128ibm/s_asinhl.c (__asinhl): Use 2**56 and
        2**-56 not 2**28 and 2**-29 as thresholds for simpler formulas.
        * math/auto-libm-test-in: Add more tests of asinh.
        * math/auto-libm-test-out: Regenerated.
        * sysdeps/i386/fpu/libm-test-ulps: Update.
        * sysdeps/x86_64/fpu/libm-test-ulps: Likewise.

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog                              |   10 +
 NEWS                                   |    2 +-
 math/auto-libm-test-in                 |   61 ++
 math/auto-libm-test-out                | 1685 ++++++++++++++++++++++++++++++++
 sysdeps/i386/fpu/libm-test-ulps        |    8 +-
 sysdeps/ieee754/ldbl-128ibm/s_asinhl.c |    8 +-
 sysdeps/x86_64/fpu/libm-test-ulps      |   27 +-
 7 files changed, 1779 insertions(+), 22 deletions(-)

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[Bug math/18020] [ldbl-128ibm] asinhl inaccurate

[jsm28 at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18020

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #2 from Joseph Myers <jsm28 at gcc dot gnu.org> ---
Fixed for 2.22.

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